The present invention relates in general to sewing machines, and in particular to a new and useful material feed device for sewing machines which includes upper and lower feed dogs, a presser foot, and means for adjusting the movements of the feed dogs and the pressure of the presser foot.
A machine is disclosed in U.S. Pat. No. 3,808,995, that is intended for sewing together sections of clothing in which, in addition to ungathered seam segments, the differential puckering or gathering of an armhole, for example, required to fit a sleeve into a finished article of clothing is also produced in the different segments of the circumference of the sleeve, in other words, ungathered seam segments alternate with seam segments with differing degrees of gather. The differential feed values can be predetermined by corresponding adjustment of the stitch guide for the size of the feed motion of the feed dog. All seam segments are sewn by this sewing machine with the same contact pressure of the presser foot adjusted to an average value based on experiential values.
Although it is known in the trade that with certain types of sewing work the best results can be obtained only with just the right pressure by the presser foot, e.g., gathered sewing must be done at very low pressure, while during ungathered segments a considerable heavier pressure is required, with conventional machines no arrangements have been made to adapt the contact pressure to the given type of sewing operation.
U.S. Pat. No. 2,544,029 does disclose a presser foot control device in which, besides a toggle lever bar operable by the usual toggle lever for reducing the contact pressure and raising the presser foot from the material, a second toggle lever, operable counter to the first toggle lever, is provided on the toggle lever bar by means of which and as needed, when sewing over cross-seams, for example, the angle position of an eccentric supporting the presser bar spring can be changed and the pressure of the presser foot thus be increased and then subsequently reduced again. The alteration and selection of the right contact pressure, however, in each case is left up to the skill and flair of the seamstress, who cannot be expected to find precisely the right adjustment required in each case repeatedly and in alternation. The operating results therefore vary a great deal.